Stator for rotating electric machine

ABSTRACT

A stator for a rotating electric machine, including an annular stator core having a plurality of slots circumferentially arranged in the stator core, and a stator winding wound around the stator core and comprised of a plurality of U-shaped conductor segments inserted in the slots and connected to each other. Each conductor segment includes a conductor and a bilayer insulative coating comprised of an insulating layer covering a peripheral surface of the conductor and a protective layer covering a peripheral surface of the insulating layer. The protective layer is formed of a material having a Young&#39;s modulus that is equal to or greater than a Young&#39;s modulus of the insulating layer at room temperature and less than the Young&#39;s modulus of the insulating layer in high temperature environments caused by heat generation of the stator winding.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority from earlier Japanese Patent Applications No. 2014-22643 filed Feb. 7, 2014, the descriptions of which are incorporated herein by reference.

BACKGROUND

Technical Field

The present invention relates to a stator for a rotating electric machine mounted in a vehicle or the like and used as an electrical motor or an alternator.

Related Art

A rotating electric machine to be mounted in a vehicle is well-known that includes a rotor, a stator core having a plurality of slots radially opposing the rotor and arranged in a circumferential direction of the core, and a stator having a stator winding wound in the slots of the stator core.

A known stator winding wound around the stator core, as disclosed in Japanese Patent No. 4450125, is a segmented stator winding formed by connecting terminals of a plurality of U-shaped conductor segments. Such a stator winding is formed by inserting a pair of straight portions of each U-shaped conductor segment into different slots from one of axial ends of the stator core, bending a pair of open end portions of the conductor segment protruding from the other axial end of the stator core in opposite circumferential directions to form a pair of angled portions, and then joining, e.g., welding, the angled portions of different conductor segments together to form a joined connection. Each U-shaped conductor segment includes a conductor and an insulative coating covering a peripheral surface of the conductor.

When, as above, the open end portions of each U-shaped conductor segment protruding from the other axial end of the stator core are bent in opposite circumferential directions with predetermined (constant) pressure to form the angled portions of the U-shaped conductor segment of the segmented stator winding, the U-shaped conductor segment will become in contact with corners where an axial end face of the stator core and inner walls of slots in which the U-shaped conductor segment is inserted meet. The insulative coating covering the peripheral surface of the conductor segment is prone to be damaged or collapsed, which may lead to insulation failure of the stator winding.

In addition, the stator winding produces heat through energization to become hot. Elevated temperature of the stator winding may cause the insulative coating of each U-shaped conductor segment to thermally expand. The insulative coatings of slot-received portions of the U-shaped conductor segment are prone to be damaged or collapsed within the slots of the stator core under stress due to a difference in the coefficient of thermal expansion between the insulative coating and the conductor of the U-shaped conductor segment. This also leads to insulation failure of the stator winding.

In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a stator for a rotating electric machine capable of preventing insulation failure of a stator winding from occurring during bending of conductor segments to form the stator winding or in high temperature environments, thereby ensuring good insulating properties.

SUMMARY

In accordance with an exemplary embodiment of the present invention, there is provided a stator for a rotating electric machine, including an annular stator core having a plurality of slots circumferentially arranged in the stator core, and a stator winding wound around the stator core and comprised of a plurality of U-shaped conductor segments. Each of the conductor segments includes a pair of slot-received portions inserted in different slots and a pair of circumferentially angled portions integrally connected with the respective slot-received portions and extending outside of the different slots. Prescribed angled portions of different conductor segments are joined at their junction end portions to form the stator winding.

The stator is configured such that each of the plurality of conductor segments includes a conductor and a bilayer insulative coating comprised of an insulating layer covering a peripheral surface of the conductor and a protective layer covering a peripheral surface of the insulating layer. The protective layer is formed of a material having a Young's modulus that is equal to or greater than a Young's modulus of the insulating layer at room temperature and less than the Young's modulus of the insulating layer in high temperature environments caused by heat generation of the stator winding.

In the embodiment set forth above, room temperature may be defined as a temperature within a range of 20±15 degrees C. (i.e., 5-35 degrees C.) in conformity to the Japanese Industrial Standards (JIS). The high temperature environments are environments caused by heat generation through energization of the stator winding during operation of the rotating electric machine can vary according to specifications of the stator or the rotating electric machine and may be defined as a temperature within a range of about 160-200 degrees C.

In the embodiment set forth above, each of the plurality of conductor segments includes a conductor and a bilayer insulative coating comprised of an insulating layer covering a peripheral surface of the conductor and a protective layer covering a peripheral surface of the insulating layer. The protective layer is formed of a material having a Young's modulus that is equal to or greater than a young's modulus of the insulating layer at room temperature and less than the young's modulus of the insulating layer in high temperature environments.

That is, the Young's modulus of the protective layer of the insulative coating is set equal to or greater than the Young's modulus of the insulating layer at room temperature. With this configuration, even when the conductor segment is in contact with corners where an axial end face of the stator core from which open end portions axially project and inner walls of the slots through which the slot-received portions of the conductor segment are inserted meet while bending the open end portions of the conductor segment to form the angled portions in room temperature environments, the corners can be prevented from biting into the insulating layer while the corners are allowed to bite into the protective layer having the Young's modulus greater than the insulating layer. This can prevent the insulating layer from being damaged and collapsed, thereby preventing the insulation failure.

In addition, the Young's modulus of the protective layer of the insulative coating is set less than the Young's modulus of the insulating layer of the insulative coating in high temperature environments caused by heat generation of the stator winding through energization thereof during operation. With this configuration, under stress exerted on the insulative coating during thermal expansion of the insulative coating and the conductor within each slot in the high temperature environments such that the insulative coating is compressed between the conductor and the stator core within the slot and at least one dimension (e.g., thickness) of the insulative coating is thus reduced by a predetermined dimension reduction through sizing deformation, the protective layer collapses, thereby releasing the stress exerted on the insulative coating. This can prevent damage to or collapse of the insulating layer, thereby preventing the insulation failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial sectional view of a rotating electric machine in accordance with a first embodiment of the present invention;

FIG. 2 is a schematic perspective view of a stator in accordance with the first embodiment;

FIG. 3 is a cross-sectional view of a conductor segment in accordance with the first embodiment;

FIG. 4 is an example of inserting conductor segments into slots of a stator core in accordance with the first embodiment;

FIG. 5 is a graph of Young's modulus vs. environmental temperature for an insulating layer and a protective layer forming a insulative coating;

FIG. 6 is a cross-sectional view of a conductor segment in accordance with a first comparative example;

FIG. 7 is a cross-sectional view of a conductor segment in accordance with a second comparative example;

FIGS. 8A-8B are axial sectional views illustrating an example of bending open end portions of the conductor segment in accordance with the first embodiment;

FIGS. 9A-9B are cross-sectional views illustrating an example of bending open end portions of the conductor segment in accordance with the first embodiment;

FIG. 10 is a schematic perspective view of conductor segments in accordance with the first embodiment;

FIG. 11 is a partial cross-sectional view of the stator in accordance with the first embodiment;

FIG. 12 is a partial perspective view of a junction-side end portion of the stator in accordance with the first embodiment; and

FIG. 13 is a partial cross-sectional view of slots in which conductor segments are to be inserted in accordance with the first embodiment.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure.

First Embodiment

A rotating electric machine 1 of the present embodiment may be used as a vehicle alternator. As shown in FIG. 1, the rotating electric machine 1 includes a stator 2 configured to act as an armature, a rotor 3 configured to act as a field, a front housing 4 a and a rear housing 4 b that are connected and secured to each other with a securing bolt 4 c to enclose the stator 2 and the rotor 3, a commutator 5 configured to convert alternating-current (AC) power into direct-current (DC) power, and others.

The stator 2, as shown in FIG. 2, includes a stator core 22, a segmented stator winding 21 formed of a plurality of conductor segments 23, and an insulating sheet member 24 for electrically isolating the stator winding 21 from the stator core 22. The stator 2 is sandwiched and secured between a front housing 4 a and a rear housing 4 b and arranged around and in spaced relationship with the outer periphery of the rotor 3 with a predetermined air gap G between the stator 2 and the rotor 3 (see FIG. 11). A detailed structure of the stator 2 will be described later.

Referring to FIG. 1, the rotor 3 is configured to rotate in unison with a shaft 33 rotatably supported by the front housing 4 a and the rear housing 4 b and includes a Lundell pole core 32 and a field winding 31. A pulley 20 is secured to the front end of the shaft 33 connected to a vehicle-mounted engine (not shown) via a belt or the like.

The Lundell pole core 32 is formed of a pair of front and rear pole cores 32 a, 32 b. The pole cores 32 a, 32 b each include six claw-shaped magnetic pole portions 32 c and are both slipped onto the shaft 33 so as to cramp the field winding 31 on both sides thereof with these claw-shaped magnetic pole portions 32 c. The field winding 31 is an insulated copper winding wound concentrically and cylindrically shaped. In the present embodiment, the pole cores 32 a, 32 b are provided with eight poles, thereby forming a 16-pole rotor 3.

An axial end face (front end face) of the front housing 4 a and an axial end face (rear end face) of the rear housing 4 b respectively have inlets 42 a, 42 b for taking in cooling air. A diagonal flow fan 35 is secured (e.g., welded) to a front end face of the pole core 32 a for radially and axially discharging the cooling air taken in via the inlet 42 a. A centrifugal fan 36 is secured (e.g., welded) to a rear end face of the pole core 32 b for radially discharging the cooling air taken in via the inlet 42 b. The front housing 4 a and the rear housing 4 b have their respective outlets 41 for discharging the cooling air facing coil end portions of the stator winding 21 projecting from both axial ends of the stator core 22.

At a rear end of the shaft 33 is provided with slip rings 37, 38 electrically connected to both ends of the field winding 31, via which electrical power is supplied from a brush device 7 to the field winding 31.

In operation of the vehicle alternator configured as above, upon receipt of rotational forces transmitted from the engine to the pulley 20 via the belt or the like, the rotor 3 rotates in unison with the shaft 33 in a predetermined direction. Application of an energization voltage from the brush device 7 to the field winding 31 of the rotor 3 via the slip rings 37, 38 during rotation of the rotor 3 activates each of claw-shaped magnetic pole portion 32 c, which provides circumferentially alternating magnetic north- and south-poles in the rotational direction. This can induce a three-phase AC voltage across the stator winding 21, which allows a predetermined direct-current (DC) to be acquired from output terminals of the commutator 5.

Specific details of the stator 2 will now be described with reference to FIGS. 2 to 13. The stator core 22 is an axial stack of annular magnetic steel plates. The stator core 22 includes an annular back core 22 a that is an outer periphery portion of the stator core 22, and a plurality of teeth 22 b that project inward in a radial direction of the stator ore 22 from the back core 22 a and are equally circumferentially spaced a predetermined distance apart from each other. The teeth 22 b and the slots 25 are alternately arranged in the circumferential direction of the stator core 22 so as to receive the multi-phase stator winding 21 in the slots 25. In the present embodiment, as an example, the rotor 3 has sixteen magnetic poles of the rotor 3. Therefore, ninety-six slots 25 are equally circumferentially spaced from each other so as to receive two three-phase stator windings 2 in the slots 25.

The stator winding 21 received in the slots 25 of the stator core 22 are formed of a plurality of U-shaped conductor segments 23 joined at their junction end portions 23 f (see FIG. 10). Each conductor segment 23, as shown in FIG. 3, is a rectangular wire with a rectangular cross section including a conductor 23 j formed of a conductive metal material, such as copper or the like, and a bilayer insulative coating 23 k covering a peripheral surface of the conductor 23 j. At the junction end portions 23 f of each U-shaped conductor segment 23, the conductor 23 j is exposed with the insulative coating 23 k stripped off. The junction end portions 23 f of the different conductor segments 23 are joined in a predetermined pattern and then insulated.

The insulative coating 23 k includes an insulating layer 231 k, as an inner layer, covering the peripheral surface of the conductor 23 j, and a protective layer 232 k, as an outer layer, covering a peripheral surface of the insulating layer 231 k. The insulating layer 231 k is formed of enamel and has a thickness of about 30 μm. The protective layer 232 k is formed of a resin, such as polyether ether ketone (PEEK) or the like, and has a thickness of about 100 μm. The protective layer 232 k is formed of a material with the young's modulus equal to or greater than that of the insulating layer 231 k at room temperature, but less than that of the insulating layer 231 k in high temperature environments.

For each U-shaped conductor segment 23, the thickness of the protective layer 232 k is set greater than a thickness reduction of the insulative coating 23 k as open end portions of the U-shaped conductor segment 23 axially projecting from the slots 25 are bent in opposite circumferential directions to form angled portions 23 e. This can prevent insulation failure of the stator winding 21 that may occur when the insulating layer 231 k is broken during bending of the open end portions of the U-shaped conductor segment 23. In addition, for each U-shaped conductor segment 23, the thickness of the protective layer 232 k is set greater than a thickness reduction of the insulative coating 23 k of each slot received portion 23 a within the slot 25 in high temperature environments. The protective layer 232 k collapses (or becomes much thin) in high temperature environments during thermal expansion of the insulative coating 23 k, thereby releasing stress exerted on the insulative coating 23 k. This can prevent damage to or collapse of the insulating layer 231 k, thereby preventing the insulation failure.

In the present embodiment, as shown in FIG. 5, the Young's modulus of the PEEK used in the protective layer 232 k is equal to or greater than that of the insulating layer 231 k within a temperature range including the room temperature (120 degrees C. or less) and less than that of the insulating layer 231 k in high temperature environments (160 degrees C. or more). The Young's modulus of enamel forming the insulating layer 231 k decreases smoothly as the temperature increases. The Young's modulus of enamel does not change as abruptly as the Young's modulus of the PEEK in any temperature range.

A conductor segment of a first comparative example as shown in FIG. 6 includes a conductor 23 m formed of copper and a bilayer insulative coating 23 n including an insulating layer 231 n covering a peripheral surface of the conductor 23 m and a protective layer 232 n covering a peripheral surface of the insulating layer 231 n. The insulating layer 231 n is formed of enamel and has a thickness of about 30 μm as in the first embodiment. The protective layer 232 n is formed of a resin, such as polyphenylene sulfide resin (PPS) or the like, and has a thickness of about 100 μm. In this first comparative example, as shown in FIG. 5, the Young's modulus of the PPS used in the protective layer 232 n is less than that of the insulating layer 231 n not only in the room temperature environments, but also in high temperature environments (200 degrees C. or more), in which the protective layer 232 k of the present embodiment is remarkably different from the protective layer 232 n of the first comparative example.

A traditional conductor segment of a second comparative example, as shown in FIG. 7, includes a conductor 23 p formed of copper and a single-layer insulative coating 23 q covering a peripheral surface of the conductor 23 p. As in the first embodiment, the insulative coating 23 q is formed of enamel and has a thickness of about 80 μm.

Referring to FIG. 4, each conductor segment 23 is U-shaped and includes a pair of straight portions 23 g, 23 g, and a turn portion 23 h connecting the straight portions 23 g, 23 g at their respective ends. The pair of straight portions 23 g, 23 g of the conductor segment 23 are inserted into two slots 25 spaced a predetermined slot pitch apart from each other from one of axial ends of the stator core 22. Thereafter, open end portions of the straight portions 23 g, 23 g axially projecting from the other of axial ends of the stator core 22 are bent in opposite circumferential directions in room temperature environments.

That is, while bending the open end portions of the straight portions 23 g, 23 g of the U-shaped conductor segment, as shown in FIGS. 8A, 8B and FIGS. 9A, 9B, the U-shaped conductor segment 23 is in contact with corners where the axial end face of the stator core 22 from which the open end portions axially project and inner walls of the slots 25 through which the straight portions 23 g, 23 g of the U-shaped conductor segment are inserted meet (for example, at A portion shown in FIG. 8B, and see also FIG. 9B) with the corners biting into the insulative coating 23 k of the U-shaped conductor segment 23. For each U-shaped conductor segment 23, the Young's modulus of the protective layer 232 k of the insulative coating 23 k of the conductor segment 23 is set greater than that of the insulating layer 231 k at room temperature, and the thickness of the protective layer 232 k is set greater than a thickness reduction of the insulative coating 23 k as the open end portions of the U-shaped conductor segment 23 are bent in opposite circumferential directions to form angled portions 23 e, which can prevent the corners from biting into the insulating layer 231 k while the corners are allowed to bite into the protective layer 232 k having the Young's modulus greater than the insulating layer 231 k. This can prevent the insulating layer 231 k from being damaged and collapsed. Therefore, the insulation failure can be prevented.

Thus, as shown in FIG. 10, the conductor segment 23 includes a pair of lineally and axially extending slot-received portion 23 a, 23 a within the slots 25 and exposed coil end portions extending circumferentially from the slots 25. The coil end portions include a turn-side end portion 23 b projecting from the slots 25 and from one of axial end sides (hereinafter referred to a first axial end side)of the stator core 22 (the rear side of the vehicle alternator 1 or the right hand side as viewed in FIG. 1) and connecting the slot-received portions 23 a, 23 a at their respective ends, and a pair of junction-side end portions 23 c, 23 c integrated with the respective slot-received portion 23 a, 23 a and projecting from the slots 25 and from the other of axial end sides (hereinafter referred to a second axial end side) of the stator core 22 (the front side of the vehicle alternator 1 or the left hand side as viewed in FIG. 1).

The turn-side end portion 23 b includes, at its distal end, a turn portion 23 h arranged in a generally V-shape through curved deformation. Each of the junction-side end portions 23 c includes an angled portion 23 e at a predetermined angle to the axial end face of the stator core 22 and a junction end portion 23 f integrated with the angled portion 23 e at its distal end through bending or flexing deformation.

Each slot 25 of the stator core 22 is configured to receive a predetermined even number (four in the present embodiment) of electrical conductors (the slot-received portions of different conductor segments), more specifically, a predetermined even number of slot-received portions 23 a of different electrical conductors. In the present embodiment, as shown in FIG. 11, four electrical conductors are arranged in each slot 25 in the following radial order from the inside: an inner-most layer, an inner-middle layer, an outer-middle layer, an outer-most layer. The stator winding 21 of a specific one of phases may be formed by connecting the four electrical conductors received in one of the slots 25 in a predetermined connection pattern.

The electrical conductors in the slots 25 are electrically connected via the turn portions 23 h of the turn-side end portions 23 b on the first axial end side of the stator core 22. A number of turn portions 23 h projecting from the slots 25 on the first axial end side of the stator core 22 form a first coil-end group 21 a (see FIG. 2). The junction-side end portions 23 c are electrically connected by arc welding the junction end portions 23 f on the second axial end side of the stator core 22. A number of junction-side end portions 23 c projecting from the slots 25 on the second axial end side of the stator core 22 form a second coil-end group 21 b (see FIGS. 2, 12).

One of the four electrical conductors in one of the slots 25 is paired with one of the four electrical conductors in another one of the slots 25 circumferentially spaced a predetermined pole pitch away from the one of the slots 25. For example, as shown in FIG. 13, the electrical conductor 231 a received in the inner-most layer of one of the slots 25 is paired with the electrical conductor 231 b received in the outer-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22. Similarly, the electrical conductor 232 a received in the inner-middle layer of one of the slots 25 is paired with the electrical conductor 232 b received in the outer-middle layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22.

Such a pair of electrical conductors are electrically connected via the turn portion 23 h of the turn-side end portion 23 b on the first axial end side of the stator core 22. More specifically, the electrical conductor 231 a received in the inner-most layer of one of the slots 25 and the electrical conductor 231 b received in the outer-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22 are electrically connected via the turn portion 23 h (231 c) of the turn-side end portion 23 b on the first axial end side of the stator core 22. Similarly, the electrical conductor 232 a received in the inner-middle layer of one of the slots 25 and the electrical conductor 232 b received in the outer-middle layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22 are electrically connected via the turn portion 23 h (232 c) of the turn-side end portion 23 b on the first axial end side of the stator core 22.

That is, the turn-side end portion 23 b integrated with the electrical conductor 231 a received in the inner-most layer of one of the slots 25 and the turn-side end portion 23 b integrated with the electrical conductor 232 a received in the inner-middle layer of the same slot 25 both project from the slot 25 in the clockwise direction of the stator core 22 on the first axial end side of the stator core 22. The turn-side end portion 23 b integrated with the electrical conductor 231 b received in the outer-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 and the turn-side end portion 23 b integrated with the electrical conductor 232 b received in the outer-middle layer of the same slot 25 both project from the slot 25 in the counterclockwise direction of the stator core 22 on the first axial end side of the stator core 22.

In addition, the electrical conductor 232 a received in the inner-middle layer of one of the slots 25 is also paired with the electrical conductor 231 a′ received in the inner-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22. Similarly, the electrical conductor 231 b′ received in the outer-most layer of one of the slots 25 is also paired with the electrical conductor 232 b received in the outer-middle layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22.

Such a pair of electrical conductors are electrically connected via their respective junction-side end portions 23 c on the second axial end side of the stator core 22. More specifically, as shown in FIG. 10, the electrical conductor 232 a received in the inner-middle layer of one of the slots 25 and the electrical conductor 231 a′ received in the inner-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22 are electrically connected by joining their respective junction end portions 23 f (232 d and 231 d′). Similarly, as shown in FIG. 10, the electrical conductor 231 b′ received in the outer-most layer of one of the slots 25 and the electrical conductor 232 b received in the outer-middle layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 in the clockwise direction of the stator core 22 are electrically connected by joining their respective junction end portions 23 f (231 e′ and 232 e).

That is, the junction-side end portion 23 c integrated with the electrical conductor 231 a received in the inner-most layer of one of the slots 25 and the junction-side end portion 23 c integrated with the electrical conductor 232 b received in the outer-middle layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 both project from the slots 25 in the counterclockwise direction of the stator core 22 on the second axial end side of the stator core 22. The junction-side end portion 23 c integrated with the electrical conductor 232 a received in the inner-middle layer of one of the slots 25 and the junction-side end portion 23 c integrated with the electrical conductor 231 b received in the outer-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 both project from the slots 25 in the clockwise direction of the stator core 22 on the second axial end side of the stator core 22.

Further, as shown in FIG. 13, the electrical conductor 231 a received in the inner-most layer of one of the slots 25 and the electrical conductor 231 b received in the outer-most layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 are parts of a larger U-shaped conductor segment 231. The electrical conductor 232 a received in the inner-middle layer of one of the slots 25 and the electrical conductor 232 b received in the outer-middle layer of another one of the slots 25 that is circumferentially spaced one pole pitch (N-S pole pitch) away from the one of the slots 25 are parts of a smaller U-shaped conductor segment 232. The larger U-shaped segment 231 and the smaller U-shaped segment 232 are two types of basic U-shaped conductor segments.

The stator winding 21 includes the multi-phase windings, in each of which the insertion and connection pattern set forth above for the basic conductor segments 23 is repeated over the slots 25 around the stator core 22. For each of the multi-phase windings, the number of coil turns around the stator core 22 is two. The stator winding 21 further includes, for each phase, deformed conductor segments (not shown, but different in shape from the basic segments) including a conductor segment integrated with a lead out from an output, a conductor segment integrated with a lead out from a neutral point, and a conductor segment having a turn portion that provides connection between the first and second turn portions. Such deformed conductor segments allow winding ends of the respective multi-phase windings to be star connected.

As above, ends of the predetermined angled portions 23 e of different conductor segments 23 are joined (e.g., welded) on the second axial end side of the stator core 22 in accordance with a predetermined electrical connection pattern. This can provide the three-phase stator winding 21 wound in the slots 25 of the stator core 22. Thereafter, for each slot 25, the plurality of electrical conductors inserted in the slot 25 (slot-received portions 23 a of the respective conductor segments 23) and an insulating sheet member 24 are secured to the stator core 22 by varnish (adhesive material) dripped down into the slot 25.

In the stator 2 configured as above, each conductor segment 23 includes the conductor 23 j and the bilayer insulative coating 23 k formed of the insulating layer 231 k and the protective layer 232 k configured such that the Young's modulus of the protective layer 232 k of the insulative coating 23 k of the conductor segment 23 is set greater than that of the insulating layer 231 k at room temperature. With this configuration, even when the conductor segment 23 is in contact with corners where the axial end face of the stator core 22 from which the open end portions axially project and inner walls of the slots 25 through which the straight portions 23 g, 23 g of the conductor segment are inserted meet while bending the open end portions of the straight portions 23 g, 23 g of the conductor segment in room temperature environments, the corners can be prevented from biting into the insulating layer 231 k while the corners are allowed to bite into the protective layer 232 k having the Young's modulus greater than the insulating layer 231 k. This can prevent the insulating layer 231 k from being damaged and collapsed, thereby preventing the insulation failure.

The Young's modulus of the protective layer 232 k of the insulative coating 23 k is further set less than that of the insulating layer 231 k of the insulative coating 23 k in high temperature environments caused by heat generation of the stator winding 21 through energization thereof. With this configuration, under stress exerted on the insulative coating 23 k during thermal expansion of the insulative coating 23 k and the conductor 23 j within each slot 25 in the high temperature environments such that the insulative coating 23 k is compressed between the conductor 23 j and the stator core 22 within the slot 25 and at least one dimension (e.g., thickness) of the insulative coating 23 k is thus reduced by a predetermined dimension reduction through sizing deformation, the protective layer 232 k collapses, thereby releasing the stress exerted on the insulative coating 23 k. This can prevent damage to or collapse of the insulating layer 231 k, thereby preventing the insulation failure.

In addition, in the present embodiment, the thickness of the protective layer 232 k of each conductor segment 23 is set greater than a thickness reduction of the insulative coating 23 k as open end portions of the conductor segment 23 axially projecting from the slots 25 are bent in opposite circumferential directions to form angled portions 23 e. This can reliably prevent insulation failure of the stator winding 21 that may occur when the insulating layer 231 k is broken during bending of the open end portions of conductor segment 23. In addition, the thickness of the protective layer 232 k is set greater than a thickness reduction of the insulative coating 23 k of each slot received portion 23 a of the conductor segment 23 within the slot 25 in high temperature environments. This can prevent damage to or collapse of the insulating layer 231 k, thereby preventing the insulation failure.

The stator 2 for the rotating electric machine of the present embodiment can prevent insulation failure of the stator winding 21 during bending of the open end portions of each conductor segment 23 or in high temperature environments, thereby ensuring good insulating properties.

Other Embodiments

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention.

In the first embodiment, the conductor segments 23 forming the stator winding 21 are U-shaped. Alternatively, the conductor segments 23 forming the stator winding 21 may be I-shaped, where angled portions 23 e are formed by bending both axial end portions of each of the conductor segments 23. This can more effectively prevent insulation failure of the stator winding 21, thereby ensuring good insulating properties.

In the first embodiment, the stator for the rotating electric machine of the present invention is applied to the vehicle alternator. Alternatively, the rotating electric machine mounted in the vehicle may be a generator, an electrical motor, or a rotating electric machine that can be selectively used as either one of the generator and the electrical motor. 

What is claimed is:
 1. A stator for a rotating electric machine, comprising: an annular stator core having a plurality of slots circumferentially arranged in the stator core, and a stator winding wound around the stator core and comprised of a plurality of U-shaped conductor segments, each of the conductor segments including a pair of slot-received portions inserted in different slots and a pair of circumferentially angled portions integrally connected with the respective slot-received portions and extending outside of the different slots, prescribed angled portions of different conductor segments being joined at their junction end portions to form the stator winding, wherein each of the plurality of conductor segments includes a conductor and a bilayer insulative coating comprised of an insulating layer covering a peripheral surface of the conductor and a protective layer covering a peripheral surface of the insulating layer, the protective layer being formed of a material having a Young's modulus that is equal to or greater than a Young's modulus of the insulating layer at room temperature and less than the Young's modulus of the insulating layer in high temperature environments caused by heat generation of the stator winding.
 2. The stator of claim 1, wherein, for each of the plurality of U-shaped conductor segments, a thickness of the protective layer is set greater than a thickness reduction of the insulative coating as a pair of open end portions of the U-shaped conductor segment axially projecting from the different slots are bent in opposite circumferential directions to form the pair of angled portions.
 3. The stator of claim 1, wherein, for each of the plurality of U-shaped conductor segments, a thickness of the protective layer is set greater than a thickness reduction of a portion of the insulative coating covering at least one of the slot-received portions within the different slots in high temperature environments. 